The present invention relates to an exhaust-gas analyzer, particularly for emissions testing of motor-vehicle engines. More specifically, the present invention is related to an analyzer having a sampling tube into which a mixture of exhaust gas and ambient air is fed through gas lines, a gas feed pump being disposed downstream of the sampling tube.
Many countries require the certification of motor vehicles, especially with respect to engine emissions. Many of the prescribed certification processes require a so-called CVS (constant-volume sampling) dilution system. In this CVS certification procedure, a sample is taken from a predetermined quantity of gas, composed of engine exhaust gas and ambient air. The ratio between exhaust gas and air changes continually because a driving cycle involves different operation modes such as acceleration, deceleration, etc., of the vehicle. Each mode results in different exhaust-gas/air ratios. In the known exhaust-gas analyzers for the CVS certification procedure, an average dilution rate has been used to determine the pollutant concentration. An average dilution rate will necessarily yield only an integrated value. An instantaneous result (in acceleration phases, for example) cannot be ascertained with such a procedure. Erroneous conclusions concerning the actual relationships therefore are not precluded.